1. Description of the Related Art
The present invention relates to a semiconductor device and a method for manufacturing the same, particularly a semiconductor device radiating excellently heat from the semiconductor device and a method for manufacturing the same.
2. Description of the Related Art
In recent years, use of IC package for portable equipment or small, hi-density mounting equipment progresses, and the conventional IC package and its concept of mounting are largely changing. These details are described in CSP technology, and mounting material and device supporting the technology—special issue of DENSHI ZAIRYO (p. 22, September 1998).
FIG. 9 is a structure adopting a flexible sheet 50 as an interposer board, a copper foil pattern 51 is put on the flexible sheet through adhesive, and an IC chip is fixed. There is a pad for bonding 53 formed at periphery of the IC chip as the conductive pattern 51. A pad for connecting solder ball 54 is formed through a conductive path 51B formed in one body (integrally) with the pad for bonding 53.
At backside of the pad for connecting solder ball 54, an opening 56 where the flexible sheet is opened, and through the opening 56, a solder ball 55 is formed. The entire body is sealed with an insulating resin 58 using the flexible sheet 50 as a board. Symbol 57 is a bonding wire.
When a semiconductor device is used as an example of circuit devices, a conventional package-type semiconductor device sealed by ordinary transfer molding is popular. This is mounted on a printed substrate PS, as in FIG. 10.
In the package-type semiconductor device, the semiconductor chip 502 is covered with a resin layer 503, and a lead terminal 504 for external connection is led out through the side of the resin layer 503.
However, the package-type semiconductor device 501 does not satisfy the requirements of down-sizing, thickness reduction and weight reduction, since the lead terminal 504 is led outside from the resin layer 503 and since the overall size of the device is large.
Accordingly, various companies have tried various structures, competing with others in order to realize down-sized, thin-walled and lightweight semiconductor devices. Recently, CSP (chip-size packages) have been developed, including wafer scale CSP of which the size is equal to the chip size and other CSP that are larger in some degree than the chip size.
FIG. 11 shows a CSP 506 that is larger in some degree than the chip size, in which the glass-epoxy substrate 505 serves as a supporting board. As illustrated, a transistor chip T is mounted on the glass-epoxy substrate 505, and this is described below.
On the surface of the glass-epoxy substrate 505, a first electrode 507, a second electrode 508 and a die pad 509 are formed; and on the back thereof, a first back electrode 510 and a second back electrode 511 are formed. Via the through-hole TH, the first electrode 507 is electrically connected to the first back electrode 510 and the second electrode 508 to the second back electrode 511. The bare transistor chip T is attached to the die pad 509. The emitter electrode of the transistor is connected to the first electrode 507 via a bonding wire 512; and the base electrode thereof is to the second electrode 508 via another bonding wire 512. Further, a resin layer 513 is formed on the glass-epoxy substrate 505 to cover the transistor chip T.
Though is has the glass-epoxy substrate 505, the CSP 506 is advantageous in that the extending structure from the chip T to the back electrodes 510 and 511 for external connection is simple and the cost for manufacturing it is low, as compared with wafer scale CSP.
As in FIG. 10, the CSP 506 is mounted on a printed substrate PS. Electrodes and wires are formed on the printed substrate PS to constitute electric circuits; and the CSP 506, the package-type semiconductor device 501 or other devices such as chip resistor CR and chip capacitor CC are electrically connected and fixed to them.
The circuit thus formed on the printed substrate is fitted in various sets.
A method for manufacturing the CSP is described below with reference to FIG. 12 and FIG. 13.
First, a glass-epoxy substrate 505 as a supporting board is prepared, and Cu foils 520 and 521 are attached to both surfaces thereof via an insulating adhesive (FIG. 12A). Next, the Cu foils 520 and 521 are partly coated with an etching-resistant resist 522, corresponding to the first electrode 507, the second electrode 508, the die pad 509, the first back electrode 510 and the second back electrode 511, and the Cu foil 520 and 521 are patterned. The patterning may be carried out separately on the face and the back of the substrate (FIG. 12B).
Next, using a drill or laser, holes for through-holes TH are formed in the glass-epoxy substrate, and these are plated to be through-holes TH. Via each through-hole TH, the first electrode 507 is electrically connected to the first back electrode 510, and the second electrode 508 to the second back electrode 510 (FIG. 12C).
Though not shown, the first electrode 507 and the second electrode 508 to be bonding posts are plated with Ni, the die pad 509 to be a die bonding post is plated with Au, and a transistor chip T is die-bonded to the die pad 509.
Finally, the emitter electrode of the transistor chip T is connected to the first electrode 507 and the base electrode thereof to the second electrode 508 via a bonding wire 512, and this is covered with a resin layer 513 (FIG. 12D).
The process gives a CSP type electric device that has the supporting board 505. In this process, a flexible sheet may be used for the supporting board.
On the other hand, a method of manufacturing semiconductor devices on a ceramic substrate is described with reference to the flowchart of FIG. 13. A ceramic substrate as supporting board is prepared, and through-holes are formed therein. Next, both surfaces of the substrate are printed with a conductive paste to form face and back electrodes thereon, and these are sintered. After this, the process of this method is the same as that of FIG. 12, until the thus-constructed structure is covered with a resin layer. However, the ceramic substrate used herein is extremely brittle and is readily cracked, different from flexible sheets and glass-epoxy substrates, and is therefore problematic in that it is not applicable to resin mold sealing. Accordingly, in this process, the substrate with necessary elements mounted thereon is potted with a sealing resin, cured and flattened by polishing it, and finally this is diced into individual chips with a dicing machine.
However in case of adopting a flexible sheet 50 as an interposer board, the flexible sheet formed on a rear surface of IC chip is very expensive, and there are problems that cost rises, thickness of the package becomes thick, and weight increases.
There is a problem that heat resistance from a back face of the IC chip to a back face of the package becomes large in a supporting board because the supporting board comprises material other than metal. For said supporting board, there is a flexible sheet, a ceramic board, or a printed board. A heat conduction path comprising material superior in heat conduction is the bonding wire 57, the copper foil 51, and the solder ball 55, the above supporting board has a structure not to radiate fully at driving. Therefore there is a problem that driving current does not flow fully because of temperature rise of IC chip at driving.
In FIG. 11, the transistor chip T, the connecting means 507 to 512 and the resin layer 513 are all indispensable constitutive elements for electric connection to external units and for transistor protection. Heretofore, It has heretofore been difficult to provide a down-sized, thin-walled and lightweight circuit device that comprises these constitutive elements.
As so mentioned hereinabove, the glass-epoxy substrate 505 used as supporting board is naturally unnecessary. However, for bonding the electrodes thereto in the process of manufacturing semiconductor devices, the supporting board is used, and the glass-epoxy substrate 505 is indispensable in the manufacturing process.
For these reasons, the glass-epoxy substrate 505 is indispensably used and it increases the production costs. In addition, since the glass-epoxy substrate 505 is thick, the circuit device comprising it is inevitably thick and is limited in point of down-sizing, thickness reduction and weight reduction.
Further, the glass-epoxy substrate and the ceramic substrate indispensably require a step of forming through-holes through which the electrodes formed on the two surfaces thereof are connected to each other, and therefore manufacturing time is long and industrial-scale mass production is very difficult.